Field of the Invention
The present invention relates to an instrumentation system and a method for maintaining the instrumentation system.
Priority is claimed on Japanese Patent Application No. 2014-004367, filed Jan. 14, 2014, the contents of which are incorporated herein by reference.
Description of Related Art
An instrumentation system, which has been built in a plant or a factory or the like, generally has a configuration that on-site devices called field devices (measuring devices, and actuators), a controller for controlling the operations of field devices, and a host device for managing and controlling the field devices and the controller are connected to one another via communication means. In such instrumentation system, the controller collects process values (for example, measured values such as pressure, temperature, flow rate) obtained by the field devices, and controls the field devices based on the collected process values under the management of the host device.
There are various field devices used for the instrumentation system depending on measuring targets and operation targets. The form of signals input to and output from the field devices also varies. For example, there are a field device for performing input and output of an analog signal, which is “4 to 20 mA” and the like, a field device for performing input and output of a digital signal, which is “24V”, a field device for performing output of a thermocouple signal, and a field device for performing input and output of a contact signal. Therefore, generally, the field device is connected to the controller via an I/O module for performing a signal conversion and a protocol conversion.
The above-described I/O module is roughly classified into one, which is connected to a field device in one-on-one relationship (one-point type), and one having a plurality of channels, each of which a field device is connectable to (multipoint type). Since the one-point type I/O module is connected to the filed device in one-on-one relationship, the maintenance is easy. However, since the large installation location (footprint) is required, the manufacturing cost increases. On the other hand, since the multipoint type I/O module is one, to which the plurality of I/O modules are connectable, the installation location and the manufacturing cost can be reduced. However, there are some cases where the maintenance becomes difficult.
Japanese Patent Application Laid-Open Publication No. 2001-100816 (hereinafter, referred to as “Patent document 1”) discloses an example of I/O module in the related art. Specifically, when the I/O module disclosed in Patent document 1 is used, the I/O module is duplicated (redundant) in order to reduce the influence of stop due to the failure. Thus, even if one I/O module fails, the operation (the operation of control loop) is continued by the other I/O module. Therefore, the reliability can be improved by making the I/O module redundant.
The above-described I/O module can be used in the redundant configuration (redundant configuration) as disclosed in Patent document 1, or in a non-redundant configuration (non-redundant configuration: single configuration). As the configuration of I/O module, one of the redundant configuration and the single configuration is selected in consideration of the extent of influence on the process due to the failure of the I/O module.
When the I/O modules having the redundant configuration are used and one I/O module fails, the operation is continued by the other I/O module in either the one-point I/O module or the multiple points I/O module. Therefore, unless both I/O modules in the redundant configuration are failed simultaneously, it is considered that the availability ratio of the whole instrumentation system does not significantly decrease.
However, when the multipoint type I/O module having a single configuration is used and the I/O module fails, it is necessary to replace the failed I/O module. Thus, even if the I/O module of only one channel fails, it is necessary to stop the operation of control loop via a normal channel. Therefore, there are some cases where the availability ratio of the whole instrumentation system decreases.
When the multipoint type I/O module having a single configuration is replaced, it is necessary to perform a prior work for preliminarily determining whether the process is adversely affected by stopping the operation of control loop via a normal channel, which does not fail, or what is a work required to prevent the diffusion of the adverse influence, or the like. Thus, when the I/O module is replaced, the above-described prior work is required. Therefore, there are some cases where the maintainability decreases.